This application claims the priority of Germany Application No. 10046854.3 filed Sep. 20, 2000 and entitled ADDITIONAL FALLBACK LEVEL FOR THE FAILURE OF, FOR EXAMPLE, ANGLE SENSORS, FOR STEER-BY-WIRE SYSTEMS NOT HAVING A MECHANICAL/HYDRAULIC FALLBACK CONNECTION by Dr. Bernd Celphas, the entire contents and substance of which are hereby incorporated in total by reference.
The present invention relates to a power-assisted steering system which allows a steering angle to be imposed by means of the steering control even if at least one electrical component fails.
A power-assisted steering system of a general type and of hydraulic design for non-trackborne vehicles is known from DE-A-19855404. In this power-assisted steering system, the steering movement of the steered wheels of the vehicle is effected by a hydraulic actuator which at any given time can be connected via a shuttle valve to one of two or more hydraulic circuits. These circuits operate in parallel and (in functional terms) in the same direction in the normal mode so that if there is a fault a change can be made to a different hydraulic circuit without any interruption occurring. To control the actuator, each hydraulic circuit includes a servo-valve which (as a function of a desired/actual comparison for the steering angle) is actuated by a control and regulating means. The control and regulating means is connected to a steering-angle actual-value emitter operated by the steered wheels of the wheel and to a steering-angle desired-value emitter which is controlled by a steering control operated at the driver end. To enable drive to be applied to it, the steering control is coupled to a xe2x80x9cfeelxe2x80x9d provider which is formed (for example) by a non-self-locking electric motor which in turn is controlled by a control and regulating arrangement. The power-assisted steering system also has at least one angle sensor which is operated at the driver end by the steering control.
DE-A-19855404 fails to disclose a power assisted steering system to enable the vehicle to continue to be steered in the event of an electrical component failure (particularly of the angle sensor or sensors which detects or detect the position of the steering control).
An object of the present invention is to provide a power-assisted steering system which allows a steering angle to be imposed by means of the steering control even if at least one electrical component fails (and in particular if one or all of the angle sensors for detecting the position of the steering control fail).
The object of the invention is achieved by a power-assisted steering system for a non-trackborne vehicle having wheels, said system comprising:
a steering control operated by a driver,
a wheel angle positioner to steer the wheels,
angle sensors to sense the position of the steering control and/or the wheels,
a feel provider to generate a feel torque to simulate a feedback of force to the steering control, the feel provider having an electric motor with at least one winding,
at least one control unit for controlling the wheel angle positioner and feel provider,
wherein in the event of failure of one or more of the group selected from at least one angle sensor, at least one control unit and the feel provider, the angle to which the steering control is turned is continuously determined from a voltage which is induced in the at least one winding by turning the steering control manually and/or from the induced current, and is used to control the steering angle.
Advantageous embodiments of this power-assisted steering system are described hereinafter.
In a preferred embodiment, the terminal or source voltage(s) (EMF) which can be picked off from the terminals of the at least one winding is used to determine or estimate the angle of the steering control and/or its angular velocity.
In a preferred embodiment, a resistor is connected to each of the terminals of the at least one winding.
In a preferred embodiment, the approximate angle of the steering control is determined starting from the last valid angle for the steering control determined by means of the angle sensors.
In a preferred embodiment, the change in the angle of the steering control is calculated from the equation
xcex94xcfx86=a*t1∫t2Udt=a*[U(t2)xe2x88x92U(t1)]
(wherein the source voltage values U(t2) and U(t1) are within a presettable range).
In a preferred embodiment, a change in angle of xcex94xcfx86=0 is set for source voltage values below a given threshold voltage.
In a preferred embodiment, for source voltage values of different sizes different constants of proportionality ai are used to calculate the change in the angle of the steering control.
In a preferred embodiment, the electric motor is a commutator motor or a DC motor.
In a preferred embodiment, the electric motor is a commutator motor and the passages through zero of the terminal voltages from the windings are monitored to allow the change in the angle of the steering control to be calculated.
In a preferred embodiment, when a first terminal voltage passes through zero, the source voltage and the direction of rotation of the steering control is determinable from the difference between the other terminal voltages and the sign of the other terminal voltages and/or the nature of the passage through zero.
In a preferred embodiment, in calculating the virtual position of the steering control, full lock for the wheels is simulated by allowing the value calculated for the angle of the steering control only to lie within specified limits.
In a preferred embodiment, as soon as the angle sensors for the steering control are again supplying valid values, the difference between a valid angle sensor value and the position of the steering control which had been determined by computation up to that point is allowed for by the control unit in its command signal to the wheel angle positioner.
In a preferred embodiment, the power-assisted steering system is a steer-by-wire steering system.
In a preferred embodiment, an additional control unit or an additional electrical circuit performs the calculation of the virtual angle of the steering control.
In a preferred embodiment, the additional control unit or the electrical circuit controls the wheel angle positioner.
In a preferred embodiment, the non-trackborne vehicle is a motor vehicle.
In a preferred embodiment, the steering control is a steering wheel.
In a preferred embodiment, the source voltages are ones that exist within the nominal speed range of the electric motor and when the nominal speed range is exceeded.
In a preferred embodiment, the motor has a large number of poles.